The invention is directed to a feed device for fuel according to the preamble of the main claim.
Feed devices for fuel of the type mentioned above in which the fuel is conveyed from a fuel tank, for example, to an injection system of the internal combustion engine of a motor vehicle are already known.
A feed device of this type is known from DE 44 44 854 A1 in which the feed pump is driven by an electric motor and the fuel flows through a preliminary filter before the feed pump and, under delivery pressure, through a main filter following the feed pump. These structural component parts are arranged in a filter pot with removable cover; the electric motor and feed pump are located in a central chamber and the main filter is located in an annular chamber arranged concentrically around the central chamber.
When mounting the feed pump in the filter pot, the greatest possible tightness must be observed between the pump parts and the filter pot housing parts. Further, in the known arrangement a relatively large initial priming quantity must first be delivered by the fuel pump before the non-return valve or check valve opens the fuel path to the main filter.
The feed device for fuel described above with the inventive features of the characterizing part of the main claim is advantageous in that a side channel pump is arranged in addition at the feed pump as a preliminary stage, the fuel being conveyed in this side channel pump to the intake or suction area of a main stage via a rise pipe in the pot housing, this rise pipe preferably being located laterally next to the pot housing.
Advantageously, in the arrangement according to the invention, only a relatively small initial priming quantity is required in the fuel tank, since the fuel is sucked in via the preliminary stage whose intake connection piece can be located close to the bottom of the tank. After the preliminary stage, the fuel flows through the rise pipe directly into the pot housing so that a check valve or the starting valve which would otherwise be necessary can be eliminated. Idle running of the pot housing is also extensively prevented at the conclusion of fuel delivery because idling is possible in this case only by way of the tight seal between the preliminary stage and the main stage, which can be prevented by optimal sealing. Also, good residual purging of the pot housing can be carried out with the invention.
By suitable dimensioning of the side channel pump, in particular with an appropriate diameter of the impeller of the feed pump, the pump capacity of this preliminary stage in the feed pump can be selected in such a way that the rise pipe is filled directly by the side channel pump.
However, it is especially advantageous when a jet nozzle is arranged between the output of the side channel pump and the rise pipe; this results in an increased filling rate of the pot housing should the delivery rate of the side channel pump be too low. The pressure in the jet nozzle can be generated in a simple manner by means of the side channel pump; the necessary pressure can be built up with great accuracy by the side channel pump acting as preliminary stage, which results in an improved pot filling rate.
To prevent fuel losses in the pot housing when the vehicle which is driven by the fuel is stopped, it is advantageous when the side channel pump is integrated in the impeller of the feed pump and when the impeller of the fed pump rests as flat as possible on a corresponding adjoining surface of a suction cover of the feed pump. Not only is an optimal sealing of the main stage achieved in this way, but the sealing of the main stage relative to the preliminary stage is also advantageously ensured. To prevent possible axial forces, pressure pockets which make it possible to compensate for axial forces through pressure differences at the impeller can also be arranged in the area of the support surfaces of the impeller, so that fewer frictional forces occur and improved efficiency is accordingly achieved.
These and other features of preferred further developments of the invention follow from the claims as well as from the description and drawings. The individual features can be realized independently or together in the form of subcombinations in the embodiment form of the invention and in other fields and can constitute advantageous constructions which are also patentable per se and for which protection is claimed herein.